The 3rd Generation Partnership Project (3GPP) is a collaboration between groups of telecommunications associations, to make a globally applicable third generation (3G) mobile phone system specification within the scope of the International Mobile Telecommunications-2000 project of the International Telecommunication Union (ITU). The following 3GPP specifications—3GPP TS 23.060 v8.1.0, 3GPP TS 23.402 v8.4.0, and 3GPP TS 23.401 v8.4.0 (which are incorporated herein by reference)—describe techniques for connecting a user equipment (UE) to an Evolved Packet Core (EPC) using either a 3GPP access or a non-3GPP access. There are various types of non-3GPP accesses—e.g., a trusted non-3GPP access and an untrusted non-3GPP access. There are also various types of 3GPP accesses—e.g., E-UTRAN, UTRAN (3G) and GERAN (2G).
In a 3GPP access network, there can be two types of Serving GPRS Support Nodes (SGSNs) deployed—i.e., the S4 SGSN and the Gn/Gp SGSN. Such SGSNs allow the UE to access the EPC via the UTRAN and the GERAN. FIGS. 1-4 illustrate various architectural models of a 3GPP network. Specifically, FIG. 1 illustrates a roaming architecture for interoperation with Gn/Gp SGSN, FIG. 2 illustrates a non-roaming architecture for interoperation with Gn/Gp SGSNs, FIG. 3 illustrates a non-roaming architecture for 3GPP accesses within EPS with the S4 SGSN, and FIG. 4 illustrates a roaming architecture for 3GPP accesses within EPS with the S4 SGSN.
The current specifications only define procedures for handover between a non-3GPP access and a 3GPP access with the S4 SGSN. FIG. 5 illustrates a conventional procedure (as described in 3GPP TS 23.402 v8.4.0) when the UE handovers from the trusted/untrusted non-3GPP access to the GTP-based S5/S8 for UTRAN/GERAN with the S4 SGSN. That is, handover between the non-3GPP access and the 3GPP access with the Gn/Gp SGSN is not supported, even though the 3GPP access network with the Gn/Gp SGSN deployed is able to re-connect the UE to the EPC. FIG. 6 illustrates a conventional combined GPRS/IMSI attach procedure 600 with the Gn/Gp based SGSN. FIGS. 7 and 8 respectively illustrate PDP context activation procedures 700, 800 with the Gn/Gp based SGSN for A/Gb mode and lu mode.